Field of the Invention
The present invention relates to a light-shielding paint used for optical devices such as cameras, binoculars, and microscopes, a light-shielding paint set, a light-shielding film and a method for producing the light-shielding film, and an optical element and a method for producing the optical element.
Description of the Related Art
Light-shielding films used for optical elements or the like are mainly films disposed on the surface of glass. Such optical elements may be lenses, prisms, or other optical glasses. Hereafter, light-shielding films will be described using a lens as an example.
As illustrated in FIG. 6, a light-shielding film 1 of an optical element is disposed in a desired peripheral portion of a lens 2. When light strikes only the lens 2 as in the case of incident light 3, the light passes through the lens 2 as transmitted light 4. When incident light 5 enters the lens 2 diagonally, the light strikes the light-shielding film 1. Herein, if the light-shielding film is not disposed (lower side of the lens in FIG. 6), the light that has struck the peripheral surface of the lens 2 undergoes internal reflection. The internally reflected light 6 unrelated to an image is emitted from the lens 2 and causes flare and ghosting, which degrades the image. When the light-shielding film 1 is disposed (upper side of the lens in FIG. 6), the internal reflection caused by the diagonal incident light 5 can be reduced. Thus, the amount of the internally reflected light 6 that adversely affects the image is reduced, and flare and ghosting can be prevented.
The light-shielding film 1 for lenses is disposed at a position at which the light-shielding film 1 is visible when a lens user sees a lens barrel. Therefore, the light-shielding film 1 needs to have high-quality appearance for a long time. Specifically, a light-shielding film having appearance which is not easily changed is required even if being used in a high-temperature and high-humidity environment.
In recent years, there have been many glasses for optical elements such as lanthanum-based glasses, titanium-based glasses, alumina-based glasses, zirconia-based glasses, fluorine-based glasses, niobium-based glasses, tantalum-based glasses, and boron-based glasses, in addition to known silica-based glasses, for the purpose of providing characteristics in terms of refractive index, Abbe number, dispersion, and the like. When a light-shielding film is formed on each of these glasses and left in a high-temperature and high-humidity environment for a long time, white spots are generated at an interface between the glass and the light-shielding film, which may degrade the appearance.
WO2013125544A (hereafter referred to as “Patent Document 1”) discloses a light-shielding film formed by curing a light-shielding paint which contains an epoxy resin and an amine curing agent and in which, for example, the equivalent ratio of the active hydrogen equivalent of the amine curing agent and the epoxy equivalent of the epoxy resin is specified. Patent Document 1 discloses a light-shielding film that is less likely to be detached in a high-temperature and high-humidity environment and has resistance to a cleaning liquid, which is achieved by increasing the cross-linking density of the epoxy resin.
However, such an increase in the cross-linking density of the epoxy resin in the light-shielding film in Patent Document 1 has limitation in terms of preventing the detachment of a light-shielding film including the generation of white spots.